1. Technical Field
Exemplary aspects of the present invention relate to a fixing device and an image forming apparatus, and more particularly, to a fixing device for fixing an image on a recording medium and an image forming apparatus incorporating the fixing device.
2. Description of the Background
Related-art image forming apparatuses, such as copiers, facsimile machines, printers, or multifunction printers having two or more of copying, printing, scanning, facsimile, plotter, and other functions, typically form an image on a recording medium according to image data. Thus, for example, a charger uniformly charges a surface of a photoconductor; an optical writer emits a light beam onto the charged surface of the photoconductor to form an electrostatic latent image on the photoconductor according to the image data; a development device supplies toner to the electrostatic latent image formed on the photoconductor to render the electrostatic latent image visible as a toner image; the toner image is directly transferred from the photoconductor onto a recording medium or is indirectly transferred from the photoconductor onto a recording medium via an intermediate transfer belt; finally, a fixing device applies heat and pressure to the recording medium bearing the toner image to fix the toner image on the recording medium, thus forming the image on the recording medium.
Such fixing device may include a fixing rotary body heated by a heater and an opposed body contacting the fixing rotary body to form a nip therebetween through which a recording medium bearing a toner image is conveyed. As the fixing rotary body and the opposed body rotate and convey the recording medium bearing the toner image through the nip, the fixing rotary body heated to a predetermined fixing temperature and the opposed body together heat and melt toner of the toner image, thus fixing the toner image on the recording medium.
Since the recording medium passing through the nip draws heat from the fixing rotary body, a temperature sensor detects the temperature of the fixing rotary body to maintain the fixing rotary body at a desired temperature. However, at each lateral end of the fixing rotary body in an axial direction thereof, the recording medium is not conveyed over the fixing rotary body and therefore does not draw heat from the fixing rotary body. Accordingly, after a plurality of recording media is conveyed through the nip continuously, a non-conveyance span situated at each lateral end of the fixing rotary body may overheat.
To address this circumstance, a plurality of heaters having a plurality of axial spans that corresponds to a plurality of sizes of recording media, respectively, may be disposed opposite the fixing rotary body. One or more of the plurality of heaters is selectively turned on according to the size of a recording medium conveyed through the nip to heat a conveyance span of the fixing rotary body where the recording medium is conveyed and not to heat the non-conveyance span of the fixing rotary body. However, the number of heaters increases as the number of sizes of recording media increases, resulting in increased manufacturing costs and increased space occupied by the heaters.
Alternatively, the fixing device may incorporate a heat shield to shield the non-conveyance span of the fixing rotary body from the heater, thus preventing overheating of the fixing rotary body. However, since the heat shield is exposed to and heated by the heater, the heat shield is subject to thermal deformation that may result in degradation of shielding and interference with the surrounding components.